From the article: Of course, there’s another possibility that takes us far beyond astronomy when it comes to making use of this important length: creating and measuring enough spin-aligned hydrogen atoms in the lab to detect this spin-flip transition directly, in a controlled fashion. The transition takes about ~10 million years to “flip” on average, which means we’d need around a quadrillion (1015) prepared atoms, k…
I’m reading that an H-maser emits 1.4GHz. Maybe you mean something besides it’s emission frequency?
1.4 GHz = 21 cm. Masers use the same transition AFAIK.
This 21-centimeter transition was chosen by the designers of the Pioneer plaques ( https://en.wikipedia.org/wiki/Pioneer_plaque ) to explain to any alien readers how big we are. At top left is a cartoon of two hydrogen nuclei in opposite spin orientations, and a ruler in between them marked "1". Over on the far right you can see another ruler that measures the height of the female figure, marked with binary numeral "…
Unsure what the tone of this message is, so I don't know if you're aware, but that's included too: > Behind the figures of the human beings, the silhouette of the Pioneer spacecraft is shown in the same scale so that the size of the human beings can be deduced by measuring the spacecraft. It's good to have redundancy, not just so someone interpreting the plaque can confirm their hypothesis, but also in case one of th…
I sarcastically referenced the plaque itself, which is a convenient disc of a known size to anyone observing the drawing, unlike the space craft or physics riddles. Using quantum transitions is quite ridiculous in my opinion due to requiring not only the observer to have a perfectly compatible understanding of physics (even a more advanced understanding might not be compatible - maybe they don't categorize elements b…
Do you think that physics is somehow subjective? We absolutely would have decoded the message.
Unsure what the tone of this message is, so I don't know if you're aware, but that's included too: > Behind the figures of the human beings, the silhouette of the Pioneer spacecraft is shown in the same scale so that the size of the human beings can be deduced by measuring the spacecraft. It's good to have redundancy, not just so someone interpreting the plaque can confirm their hypothesis, but also in case one of th…
I sarcastically referenced the plaque itself, which is a convenient disc of a known size to anyone observing the drawing, unlike the space craft or physics riddles. Using quantum transitions is quite ridiculous in my opinion due to requiring not only the observer to have a perfectly compatible understanding of physics (even a more advanced understanding might not be compatible - maybe they don't categorize elements b…
I submit that if the concept of quantum transitions is alien to whatever recipient of that probe (if ever), then any attempts to communicate are hopeless anyway. That is, if the recipient's physical reality is so different from our own that they can't at least get back to "oh, this distance means that transition, now the rest of the plaque makes sense", then no asynchronous communication will bridge that gap.
It's ruled out by the signal being modulated. The question the choice is answering is where do you put a signal where other intelligent minds might look for it, yet which isn't at a frequency where the universe is particularly loud in ways that will make detecting your signal harder.
The signal is always going to be modulated, unless the source is maintaining a position with zero relative velocity to the Earth, or deliberately compensating for same - both of which would be far more impressive as a "hello" than a random-ish number which will always be distorted by orbital and proper motion. Otherwise it's going to have a varying frequency - maybe not by much, and maybe not quickly, but certainly n…
Fair, I should have said "modulated by something other than obvious physical processes".
I find it disturbing/puzzling that there is this fundamental physical behaviour like emission of light with wavelength of _exactly_ 21cm -- assuming one centimeter wasn't based on any such property but was just a "random" unit measure that stayed with us historically and through sheer volume of use (in U.S. inches filled the same niche; still do). I mean what are the odds that the wavelength is _exactly_ (the word us…
isn't a cm now defined based on the distance light travels in a vacuum in a very small period of time? so it's not arbitrary really, or rather it probably goes the other way around. a cm used to be based on an arbitrary physical distance but was I think redefined to avoid needing to keep a standard meter cube in Paris.
The standard metre was a rod 1 metre long, you might be thinking of the standard kilo which is a compact cylinder?
Amazing article! It seems incredibly to weird to hear about transitions causing photons at 21cm wavelength; I guess I'm only used to seeing (no pun intended) much shorter wavelengths at hundreds of nanometers.
Yeah, it's weird to me that an atomic transition can create something with a wavelength so much longer than the atomic radius. (Yeah, I know that it's a really low-energy transition, and I know about the relationship between energy and wavelength. But the net result I still find highly counter-intuitive.)
It started with the grandfather clock. Everyone's clock pendulum needed to be the same length to have the same length of a second. So a meter also happens to (approximately, this was before we could easily be precise to several decimal places) be the length of pendulum that cycles at 0.5 hz (each swing back and fourth is a second) in 9.8 m/s^2 gravity.
It started with the French. https://en.m.wikipedia.org/wiki/History_of_the_metric_system The meter was originally based on the measured dimensions of the Earth.
Ah yes, you're right. Another nice coincidence that a seconds pendulum is less than 1% away from 1/10 millionth the distance between the equator and poles.
This 21-centimeter transition was chosen by the designers of the Pioneer plaques ( https://en.wikipedia.org/wiki/Pioneer_plaque ) to explain to any alien readers how big we are. At top left is a cartoon of two hydrogen nuclei in opposite spin orientations, and a ruler in between them marked "1". Over on the far right you can see another ruler that measures the height of the female figure, marked with binary numeral "…
If only we could somehow share a physical entity of known dimensions to reference together with the drawing so that we did not need to use a physics riddle to indicate scale...
Yeah. It would be pretty funny if an alien reader of the plaque concluded that 1 refers to the actual length of the line between the two circle thingies and concluded, therefore, that we're only a few cm tall.